三角函数诱导公式化简2题.
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三角函数诱导公式化简2题.
sin(-1071°)×sin99°+sin(-171°)×sin(-261°)
1+sin(α-2π)×sin(π-α)-2cos^2(-α)
sin(-1071°)×sin99°+sin(-171°)×sin(-261°)
1+sin(α-2π)×sin(π-α)-2cos^2(-α)
![三角函数诱导公式化简2题.](/uploads/image/z/18554675-59-5.jpg?t=%E4%B8%89%E8%A7%92%E5%87%BD%E6%95%B0%E8%AF%B1%E5%AF%BC%E5%85%AC%E5%BC%8F%E5%8C%96%E7%AE%802%E9%A2%98.)
sin(-1071°)=sin(-360*3+9)=sin9
sin99°=cos(90-99)=cos9
sin(-171°)=sin(-180+9)=-sin9
sin(-261°)=sin(-360+99)=sin99=cos9
原式=sin9cos9-sin9cos9=0
sin(α-2π)=sinα
sin(π-α)=sinα
1+sin(α-2π)×sin(π-α)-2cos^2(-α)
=1+sin^2(α)-2cos^2(α)
=1+(1-cos2α)/2-(1+cos2α)
=1/2-3/2cos2α
sin99°=cos(90-99)=cos9
sin(-171°)=sin(-180+9)=-sin9
sin(-261°)=sin(-360+99)=sin99=cos9
原式=sin9cos9-sin9cos9=0
sin(α-2π)=sinα
sin(π-α)=sinα
1+sin(α-2π)×sin(π-α)-2cos^2(-α)
=1+sin^2(α)-2cos^2(α)
=1+(1-cos2α)/2-(1+cos2α)
=1/2-3/2cos2α